1. Field of the Invention
The present invention relates to data-communication apparatuses and methods, and in particular, to a data-communication apparatus and method for performing data communication by using a modem with a plurality of modulation/demodulation modes which is controlled by the data-communication apparatus to modulate/demodulate signals in a mode specified from among the modulation/demodulation modes.
2. Description of the Related Art
Conventional data-communication apparatuses of this type include, for example, a facsimile apparatus. Concerning the facsimile apparatus, increasing its transmission speed is in progress. The International Telecommunications Union (ITU) has recommended a communication protocol (V.34) using a V.34-modem with a maximum transmission speed of 33.6 kilobits/second (kbps) which exceeds the 14.4 kbps obtained by a conventional V.17-modem, and the V.8 protocol for specifying a modem to be used when line connection to another unit is established. The V.34 protocol and the V.8 protocol will be hereinafter treated as new protocols. Although increasing the transmission speed is effective in reducing communication costs, it is required that a facsimile apparatus as a communication apparatus have a protocol capable of achieving a faster transmission speed, and maintain compatibility with conventional facsimile apparatuses.
When performing automatic reception, a conventional facsimile apparatus having both the new and conventional protocols sends a signal ANSam (representing the V.8 protocol and being a 2100-Hz modified tone) compatible with the conventional protocol signal CED. When the other apparatus receives the signal ANSam, it sends a new protocol signal CM (which is a call-activation menu signal, which is used to represent a usable modulation method, and which is a 300-bps signal modified in the V.21 low-range channel). When the facsimile apparatus receives the signal CM within a reference time, it sends a signal JM (which is a common menu signal and is a 300-bps signal modulated in the V.21 high-range channel) representing a usable modulation method for both apparatuses, based on the signal CM and its own function. On receiving the signal JM, the other apparatus sends a signal CJ (which represents a termination of the signal CM and is a 300-bps signal modulated in the V.21 low-range channel). In this manner the facsimile apparatus communicates with a modem using the modulation method represented by the signal JM. Half-duplex communication with the V.34-modem, designated by the signal JM, shifts the protocol for the facsimile apparatus to the V.34 protocol. In addition, when the facsimile apparatus sends the signal ANSam, and cannot receive the signal CM within the predetermined time, it determines that the other apparatus is a conventional one, and transmits a conventional signal DIS in the T.30 protocol which is modulated in the V.21 high-range channel. The facsimile apparatus receives a signal DCS modulated in the V.21 high-range channel.
When the other apparatus performs manual transmission, and starts a transmission operation after the signal ANSam ends, it does not send the signal CM and the signal CJ. Accordingly, the facsimile apparatus sends the conventional T.30 protocol signal DIS. In this case the signal DIS is sent, with the signal DIS being provided with information representing possession of the V.8 protocol-functions so that the T.30 protocol can shift to the new protocol. The signal DIS causes the other apparatus to recognize that the receiver apparatus has the V.8 protocol. If the other apparatus has recognized that the receiver apparatus has new protocol functions, it sends a signal CI (being a call-activation display signal and a 300-bps signal modulated in the V.21 low-range channel) representing a return to the V.8 protocol. If the other apparatus has recognized the receiver apparatus has no new-protocol functions, it sends a signal DCS (300-bps signal modulated in the V.21 high-range channel) in the T.30 protocol.
In order to cope with the above circumstances, the receiver apparatus must have a structure capable of simultaneously detecting the signal CI modulated in the V.21 low-range channel (L) and the signal DCS modulated in the V.21 high-range channel (H).
Conventionally, the two channels: the V.21 low-range channel (L) and the V.21 high-range channel (H) are used for full-duplex communication. Conventional facsimile apparatuses use the V.21 modem for only half-duplex communication, and have no structure capable of simultaneously receiving signals in the two channels. In other words, setting the V.21-modem in the high-channel mode (H-channel mode) for receiving the signal DCS hinders the V.21-modem from receiving the signal CI in the low-range channel. Also, setting the V.21-modem in the low-range channel mode (L-channel mode) for receiving the signal CI hinders the V.21-modem from receiving the signal DCS in the high-range channel.
To overcome this problem, by using a plurality of V.21-modems, it is possible that one end receives a signal in the low-range channel and another end receives a signal in the high-range channel. However, such a structure is complicated.